Some were outraged. A profile in Life magazine in 1964 asked if he was "the worst artist in the US." But Lichtenstein was soon a household name, his work hanging in major museums, his paintings fetching record prices.

And yet, as a new retrospective at London's Hayward Gallery reveals, the Pop Artist seemed to run out of steam. While rival Andy Warhol kept the faith and reaped the celebrity, Lichtenstein delved deeper into formalist concepts about art that mystified even the avant-garde.

By the 1970s, he was training his eye on the legends of modern art, fusing his own motifs (Swiss cheese, a folding chair, a piercing shade of yellow) with those of Picasso, Matisse, and Magritte to produce work best described as perplexing.

"There's no question that his Pop work from early 1960s is very important," says British art critic Jonathan Jones, "but he seemed a bit insecure in moving on quite quickly to do art which was showing off its own cleverness - art about art. This retrospective makes him seem a one-note artist."

Lichtenstein was born in Manhattan in 1923 and fought in Europe in World War II. He was almost 40 when he produced his breakthrough piece, a reproduction of Mickey Mouse and Donald Duck depicted in flat, almost machine-printed form. The stark piece with its silly caption (Look Mickey, I've Hooked a Big One!!) and its corny joke (Donald has actually hooked his own coat) brought out the vulgarity in an all-American icon, albeit in an affectionate way.

There followed a succession of pieces drawn from magazine ads and comic strips that contrasted the material comfort of the postwar boom with the emotional vacuity of the times. America, he seemed to be saying (with several exclamation marks), have your washing machines and new bathrooms, but look how bland and sterile it all is.

A series of comic-strip romances, in which a clichéd female figure is at the mercy of a stereotypical alpha male, betrays a troubled take on relationships, while perhaps his best-known work, "Whaam," amplifies the frivolous way that war is viewed, putting the casual into casualty.

"With pieces like 'Whaam,' you can see more sociopolitical comment [and] protests against the war; and other works show a protest of gender issues," says British art historian Ben Jones. "But Lichtenstein had something to say about the form of painting as well as about the times in which he lived."

Indeed, Lichtenstein himself was interested more in the formal qualities of these images rather than in their subject matter. As he once said, "All my art is in some way about other art, even if the other art is cartoons." By the late 1960s it was no longer cartoons, but landscapes, interiors, and still life that Lichtenstein explored, his trademark techniques always suggesting the artificial, the phony.

"Lichtenstein's real subject was the transformation of the original image into a painting rather than the content of the image itself," says Martin Caiger-Smith, exhibitions director at the Hayward.

He was fascinated by how visual constructs, such as diagonal lines representing mirrors, could deceive the viewer. "I show you the traps you fall into when you believe the things that are painted are real," Lichtenstein once said.

The content may seem dated, but younger artists still find a relevance for today's overproduced age.

"We are at a point in time in society where virtually everything we see, we see through reproductions," says Diane Waldman, formerly of the Guggenheim, in the exhibition's audiovisual presentation. "Why not make an art that reflects that?"